Note: Descriptions are shown in the official language in which they were submitted.
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
A DEVICE WITH SIGNAL GENERATOR AND SIGNAL RECEIVER FOR
PROVIDING CONTROLLED ACCESS TO INFORMATION AND/OR COMMUNICATION
CHANNELS
FIELD OF THE INVENTION
The present invention relates to the field of remote controls for electronic
devices.
BACKGROUND OF THE INVENTION
Remote control systems, including devices with a signal generator and a signal
receiver for
providing controlled access to information and/or communication channels,
whereby signal
generator and signal receiver are set to transmit and receive an infra-red
signal or radio signal,
respectively, and the signal receiver is set to provide access to the
information and/or
communication channels on receiving the signal, are known. Suitable
information and/or
communication channels include the entire range of radio, television, film
channels and video
channels, plus all possible data channels. Remote controls are also known for
toys, computers,
consumer electronics, automobiles, etc.
Such a device is in itself known and is widely used in combination with
providing paid
acccss to television channcls or film channels in hotel rooms, for example. By
using an appropriate
computcr system, it is possible to monitor how long and which television
and/or film channels are
watched and whether an Internet connection is used, for example. Besides the
fact that such
systems are particularly expensive, the disadvantage of such a system for the
hotel guest is that
his/her privacy can easily be invaded. In particular, the log of hotel guest
activities may be an
invasion of privacy, and the distribution of that log as part of a bill
problematic.
Another known, simpler system allows the hotel guest to rent an operating unit
when he/she
registers at the hotel reception desk, and provides the hotel guest access to
the available information
and communication channels during his/her stay. Such a system has the
disadvantage that careful
administration has to be kept of who has been provided with such an operating
unit, whether the
operating unit has been returned and whether it has actually been paid for.
The transport of the unit
also opens it to possible theft or damage.
Micropayment technologies are known which allow, using cryptographic security,
a
reasonably secure payment to be made without requiring real-time verification.
Some of these
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-2-
technologies also allow re-spending of received value. See, e.g., US Pat. No.
5,999,919 expressly
incorporated herein by refcrence. See also Rivest and Shamir, "PayWord and
MicroMint: Two
Simple Micropayment Schemes" (May 7, 1996), all of which are expressly
incorporated herein by
reference.
Rolling code technologies provide a method for cryptographically communicating
using a
cryptographic scheme which changes with use or time. The encryption key seed
and decryption
key seed each advance incrementally and a re kept in synchronization. Thus
defeats replay attacks,
since old messages no longer have the proper cryptographic properties. See,
e.g., US Pat. Nos.
7,050,947; 6,980,655; 6,900,720; 6,882,729; 6,810,123; 6,690,796; 6,323,566;
6,249,582;
6,225,889; 6,194,991; 6,154,544; 6,078,271; 6,046,680; 6,028,527, each of
which is expressly
incorporated herein by reference.
Challenge Response technologies require a two-way communication between two
systems
which seek to communicate. Typically, one system seeks to authenticate the
other, but the
technology is also capable of authenticating both systems to each other. DTCP
(content protection
for IEEE-1394) employ such technologies. See, e.g., US Pat. Nos. 7,051,212;
7,025,209;
7,010,692; 6,981,145; 6,850,252; 6,792,533; 6,640,304; 6,607,136; 6,427,140,
expressly
incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention is intended to provide a system with which the above
disadvantages
of these known systems can be overcome. Correspondingly, according to the
invention, the wireless
signal generator will be set to transmit an encoded signal which limits a
number of times a service
may be operated and/or a time period over which such services may be operated.
For example, a hotel guest may wish to purchase a pay per view movie for
single viewing,
without that transaction appearing on the hotel bill. The guest acquires an
encoded device which
carries with it the right to activating the pay per view service, but cannot
be used more that the
predetermined limit. The device can preferably be transferred, and thus the
acquisition of that
device may be anonymous. Likewise, the use of that device may be self-
authenticating, and
therefore detailed logs need not be maintained or analyzed for real-time
billing purposes. Typically,
a log is maintained for royalty auditing, but the audit log may be anonymous
or even aggregated
data.
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-3-
According to an embodiment of the present invention, the signal generator will
be set to
transmit a predetermined signal comprising simultaneous transmission of two or
more different
codes once only or for a previously-determined time, to a programmed signal
receiver, e.g., in a
hotel television, which is able to accept these codes simultaneously and
provides direct access to
the available information and communication channels. For example, the Philips
iTV platform is
capable of receiving multiple signals simultaneously. The use of the
simultaneously transmitted
signals discourages the use of signal recording devices to replay the signal,
and thus permit
unauthorized use of the programmed signal receiver. Of course, this technique
can only be used in
conjunction with signal receivers which simultaneously receive the signals for
processing.
One embodiment of the invention therefore provides a signal generator embodied
as a
disposable product in the form of a small remote control with volume (up and
down) and channel
(up and down) buttons, that can only be used once or for a limited period.
This has the advantage
that no administration at all has to be kept, and that there is absolutely no
invasion of the hotel
guest's privacy. The fact that the signal generator according to this
embodiment of the present
invention transmits a predetermined signal of two or more different codes
once, to a programmed
signal receiver in the hotel television, makes it difficult or impossible to
access the available
information and communication channels otherwise.
In order to permit the signal generator be suited for limited usage, the time
during which the
previously-determined signal is capable of being transmitted may be limited to
a short period
required to control the signal receiver within the scope of intended or
authorized usage. For
example, a single usage activation device may be provided. Here, account must
be taken of the fact
that the signal generator must be properly set and that the hotel guest is not
acquainted with its
specific equipment and set-up. The time the device is operational will
therefore be in the order of
several seconds to several minutes and more preferably in the order of 10 to
60 seconds. In
practical tests, an operational time of 25 to 35 seconds appeared to be amply
sufficient.
According to one embodiment, the signal generator is provided with a signal
source for
generating two or more codes simultaneously, a power source and a contact
switch for the
connection of the power source, whereby the capacity of the power source is
such that the
predetermined signal can be transmitted for the predetermined time. With this
embodiment, the
time is determined by the capacity of the power source and the power
consumption of the signal
generator and remainder of the device. If the signal generator has a variable
power consumption, it
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-4-
is also possible to provide a constant load across the power source after
activation, which will drain
the power source after a prcdctermined period of time.
Although the available usage time can be reasonably determined with such a
circuit, it is
possible that a signal generator that has been in stock for a long time will
have a reduced power
source capacity such that the available operating time is insufficient. It is
therefore preferable to
have an embodiment whereby the signal gencrator is provided with a power
source, a contact
switch and a programmable integrated circuit, whereby the predetermined signal
to be transmitted
and the time that the signal is to be transmitted are programmed. Here, there
is a provision that the
program included in the programmable integrated circuit is triggered by the
first closing of the
switch.
With such an embodiment, the time that the signal is transmitted can be
determined quite
precisely in the software, and the time does not generally depend on a power
source capacity
(which may have a surplus) that is not exactly known.
In order to ensure that the signal generator can no longer be used after the
programmed time
has expired, another embodiment provides a means for interrupting the signal,
by using the
program. Instead of interrupting the signal, the program can be so set that
the signal of two or more
codes transmitted is changed and is not recognized by the signal receiver. In
both cases, reuse of the
signal generator for its original purpose is in fact no longer possible. This
can be improved on by
providing that running through the program ends with the total deletion of the
relevant program
data, that is, the program data is stored in volatile memory which is modified
during execution.
Thus, another type of security may be provided, or triggering of a fuse to
permanently inactivate
the device or make functions inaccessible. For example, premium channels may
be limited to a set
duration, while other functions, such as volume, and non-premium channels, may
be accessible
without restriction. Indeed, this embodiment permits a pre-purchase of pay per
view content,
activated by a pressing a button on the device, and which after a
predetermined number of presses,
becomes exhausted.
An embodiment of the invention may therefore provide the signal generator with
a power
source (such as an electrochemical battery, zinc-air battery, capacitor, or
fuel cell), a contact switch
and a programmable integrated circuit, whereby the previously-determined
signal to be transmitted
and the time that the signal is to be transmitted are programmed. Here, there
is a provision that the
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-5-
program included in the programmable integrated circuit is triggered by the
first initiation of
contact of the switch. This embodiment is generally consistent with a
relatively simple device
which transmits a static identification code which directly authorizes the
receiver, rather than an
embodiment wherein the management system receives a signal from the device,
through the
receiver, and then authorizes usage.
Furthermore, the device can preferably be provided with a contact that can be
set from an
unconnected state to a connected state once only for the connection of the
circuit to the power
source. As a result, the power source can be kept at sufficient capacity as
long as possible and
undesired signal generator operation can be prevented. As an alternate to the
contact,
advantageously a zinc-air battery is employed, which is activated by exposing
the cell to air by
removing a barrier. Once this electrochemical reaction starts, it will
typically exhaust the battery
over a relatively short period.
Besides the device with signal generator and signal receiver, the present
invention also
relates specifically to the signal generator itself, whereby the signal
generator comprises a housing
that accommodates a programmable integrated circuit, a power source, a control
to transmit the
programmed signal (e.g., comprising a plurality of simultaneously transmitted
components) and a
switch to start the program that is saved in the integrated circuit. Here, the
signal generator is
preferably further provided with a removable interrupter in the connection of
the power source to
the integrated circuit.
It should be clear that the signal generator according to an embodiment of the
invention can
be offered in many different ways because it is a disposable (throw-away)
product for once-only
use that cannot inherently be administratively connected to the user in any
way. This is an
important aspect of this embodiment of the invention, and its use as such with
offering the signal
generator is therefore part of the invention.
The invention also provides a method for marketing the signal generator that
is mainly
characterised by offering the signal generator through free sales channels,
e.g., at no immediate cost
to the user. According to another embodiment, the signal generator is offered
for sale through a
vending machine. Here, one can think of a vending machine for sweets and soft
drinks, with one
segment of the vending machine being reserved for an array of signal
generators, for example. In
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-6-
this way, the signal generator is offered for sale completely anonymously and
the consumer can
buy a signal gcnerator at any desired moment.
Besides this, the signal generator can also be offered for sale at a hotel
desk or in a minibar
in a hotel room. In this way, it is known that a hotel guest has bought a
signal generator; however,
his/her privacy is still generally preserved with regard to his/her viewing
and listening behaviour.
The method according to the invention further provides the possibility of
offering the signal
generator as a promotional product. Here, we can think of travel agencies or
other companies in
service industries allied to the hotel, such as car hire companies and
restaurants.
Finally, the method according to the invention also provides the possibility
that the signal
generator can carry one or more advertising slogans. Besides being able to put
logos and brand
names on the signal generator, it is equally possible to make the external
appearance of the signal
generator such that it (largely) corresponds with the product or logo design
of the company making
the advertisement.
According to another embodiment, the device presents a self-authenticating
signal, which
changes dynamically, and is not subject to replay attacks, since devices can
be created to capture
infrared or RF signals and reproduce these idcntically. Thus, once a signal
sequence is employed,
that particular sequence must be deauthorized for future use. In the case of a
limited time signal,
two particular options are preferred. First, a rolling code algorithm may be
employed, in which
each use of the device resets the code (and the corresponding authentication
of the next transmitted
code). Such rolling codes are well known in the art. A rolling code system may
thus be
implemented which provides secure authentication and communication of a
message, and which is
immune to replay attacks. This requires synchronization between the
transmitter and receiver,
which may be achieved by providing, for example, a photodiode (or may employ
the normally
transmissivc LED as a photodiode) in the device which receives an optical
signal from a television
screen.
According to another embodiment, a micropayment system is implemented in which
"credits" stored in the device are transferred to the device to be controlled
through a
cryptographically secure means. Thus, the transmitter device includes prepaid
credits which are
then spent during the course of communications with the device to be
controlled, e.g., a set top box
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Onu-izap-201 PCT
-7-
or television. A micropayment is transferable, and relatively anonymous, since
the value is verified
principally through cryptographic mcans. Means may also provided to ensure
that the same credit is
not transferred twice from the same (or counterfeit) source.
While many aspects of the present invention obviate the need for a real-time
accounting and
mangement system, in some cases this may be employed. Typically, the
accounting and
management systems communicate in a real-time with a facility management
system, such as is
provided by On Command Corporation, Denver CO. Thus, a predetermined and/or
cryptographically defined code may be communicated from the device, received
by a set top box or
other receiver, and communicated to a management system for authentication.
Since, in a preferred
embodiment, the device is permitted prepaid usage, and is anonymous, the
management system
authenticates that the device transmits an appropriate code, and either itself
contains usage
restrictions, or the usage restrictions are imposed by a database indexed by
the device identification.
After authentication, it is not necessary to link a certain transmitter device
to a particular receiver,
and thus anonymous statistics may be maintained for auditing, etc.
One way to provide self-authentication without need for remote management is a
challenge-
response algorithm. For example, the device may include a photodiode receiver
(or indeed, may
employ the same light emitting diode as used for transmission as a photodiode
element, see
www.sensorsynergy.com/helpfulhints.htm) which reads optical data transmitted
from a television
screen. This "challenge" signal is then processed in the device according to a
secret algorithm, to
produce a "response" signal to the receiver. The receiver then compares the
received "response" to
the anticipated "response" based on the challenge, and thus authenticates the
secret algorithm. This
algorithm, in turn, may be stored in tamper-resistant, volatile memory, and
thus the "secret"
protected. Further, the algorithm may be periodically updated in both the
receivers and devices,
limiting the harm if the secret becomes breached. See Challenge Response
security references cited
above, each of which is expressly incorporated herein by reference.
The single use only character of a preferred embodiment of the signal
generator according
to the present invention that makes it a particularly attractive commercial
product in many aspects.
Another embodiment of the invention provides a relatively full-function remote
control with
a durable power source, which is not constrained in its use by power supply.
Thus, the device may
provide sufficient power for normal operation over 1, 4, 7, or 14 days, or
longer. In this case,
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-8-
restrictions are imposed logically, rather than physically. For example, a
timer or clock may be
provided within the device to determine when it is first activated, and
provide a set of functionality
dependent on that time. The device is normally activated by removing a battery
insulator, though it
can be activated by an electronic signal or the like. For example, it may be
desired to limit the use
of the device for a period after distribution. Thus, the device may be
activated upon distribution,
for example by separation from a carrier, and then operate for 1, 4 or 7 days
thereafter. Alternately,
the device may be activated upon or in conjunction with its first use.
The invention may also be implemented using a smart card or other information
carrier
which is supplied to a persistent device, such as a remote control or a set
top box. For example, a
remote control device is provided with a card reader, which may be a smart
card (i.e., a thin carrier
device with an electrical connector or electromagnetic communication interface
between a secure
processor embedded within the carrier), optically or magnetically encoded
pattern, or otherwise
having a readable code which is reasonably authenticatable and counterfeit
resistant, which is read
by the device. The infonnation on the carrier activates all or a portion of
the functions available
through the remote control or set top box, thus alleviating the need for
remote access control and
permitting broadcast of the program material to the receiver without
implementing selective access
technologies for all channels, and thus not requiring external communication
of the identification of
the program material in some cases. The carricr may be sized similarly to a
credit card, though
other form factors may be usable, such as SD or mini-SD memory cards, SIM
cards, CF, XD, or
other known form factors. The remote control may be similar in form factor to
existing remote
controls, e.g., sized to be held and activated with a single child or adult
human hand.
The function of the card is, for example, to securely activate a timer, which
may be
implemented in a smart card in the carrier or within the remote (or in the set
top box) to watch
premium programming such as pay-tv, for a limited time, and thereafter
restrict viewing or tuning
or program selection.
The system therefore supports a business model in which the information
carrier authorizes
a predetermined time of viewing, without providing any persistent association
of an identification
of the viewer and the content being viewed, and thereby ensuring privacy.
According to one embodiment, an accounting system may be supported which
automatically activates and accounts for the card when first used. This, for
example, requires
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-9-
sending a signal from the carrier, through the remote control, to the
receiver, and hence to a remote
servcr. This scheme, while adding a lcvcl of complexity to the infrastructure,
permits
compensation for the carrier based on actual usage, and compensation of the
content owners of pay-
per-view programming based on actual viewing. This extended infrastructure,
which is not
generally required by other embodiments of the invention, may be used to
ensure that the carriers
are authentic and properly paid for, since duplicate usage or spurious
authentication requests could
be readily identified. For cxample, a vendor of a carrier may be charged for
the inventory only as
the carrier is used, and therefore wide distribution of the carriers to many
vendors is encouraged.
Such accounting may be accomplished by communicating to a central server the
identification of a
carrier when it is first employed, or each time it is employed, to then bill
the account of the seller.
Assuming that the carrier itself is acquired anonymously, and the set top box
does not reveal the
information presented, privacy is preserved. However, an encrypted or secure
identification or
identification protocol may be provided as necessary to ensure system
security, protected from
availability under normal circumstances.
In other embodiments, the carrier which operates in conjunction with a durable
remote
control, or a disposable remote control device, directly activate and control
the media device, e.g.,
television, and do not necessarily interact with other remote systems, thus
permitting compensation
for the activation of the programming services without diminishing privacy by
explicitly
idcntifying the programming serviccs on a hotel bill or by linking a room
number with the
programming presented. Circumvention resistance is typically obtained by using
a non-ubiquitous
communication protocol between the remote control and the media device, and
therefore preventing
use of unauthorized third party remote controls that circumvent limitations.
Counterfeiting
resistance may be obtained cryptographically or by employing proprietary
electronics. Thus, in
such embodiments, for example, the remote control is activated by the
information carrier (e.g.,
activation card), by pulling a tab at the back if it is a key-seize remote,
etc., and simply pointed at
the infrared receiver window of the television, which responds to the remote
if within its
authorization parameters, e.g., time window of opcrability.
An embodiment therefore provides a remote control device, comprising a housing
having at
least one user interface control inputs, a self-contained power source, a
transmitter adapted to
transmit a remote control signal corresponding to an activation of the at
least one user interface
control input, and a detachable authorization information carrier, wherein a
non-consumed
detachable authorization information carrier provides authorization for a
limited quantity of usage,
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-10-
which is consumed by such use, and wherein a consumed detachable authorization
information
carrier does not provide authorization for usage. The detachable authorization
information carrier
may comprises a smart card. The detachable authorization information carrier
may be consumed,
for example, by an alteration of electronically stored information therein.
The detachable
authorization information carrier may comprise a cryptographic information
processor and an
electronic memory. The quantity of use may comprise a predetermined duration
and/or a
predetermined number of uses. The transmitter may comprise at least one
modulated infrared
optical signal generator. The detachable authorization information carrier may
be authenticated by
a process comprising receiving a challenge signal from a processor in the
housing, processing the
challenge signal in the detachable authorization information carrier according
to a secret algorithm
to produce a response signal, transmitting the response signal to the
processor to be controlled with
an usage limitation, authenticating the response signal and usage limitation
in the processor, and
selectively activating the transmitter in accordance with the usage
limitation, wherein the usage
limitations represents a prepaid compensation for controlled access to a
device to be controlled by
the transmitter.
The device may be multifunctional, and for example, serve as a complete or
supplemental
remote control for a device, such as a video tuner. For example, the device
may include buttons for
volume control (+/-), channel (up/down), on/off, mute, etc. The device, for
example, may be
programmcd to provide a set of activations for premium programming, i.e., pay
per view. Thus, the
device may have a button for activating a pay per view channel. The device may
be
preprogrammed to provide a limited number or duration of such activations.
Thus, billing for such
programs need not appear on a hotel bill, for example, since the accounting is
separate and prepaid.
The present invention therefore provides a relatively anonymous method for
prepaid
authorization of functioning of an electronic system, which avoids the need
for an express
accounting log of usage to verify charges. Thus, user privacy is enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further elucidated on the basis of the example given
in the
drawings, where:
Fig. 1 shows a schematic diagram of a device having a signal generator and
signal receiver
according to the present invention, and
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-11-
Fig. 2 shows the signal generator according to Fig. 1 schematically in more
detail.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows a schematic diagram of an embodiment in which an interruption
and/or
distortion unit 4 is included in a number of incoming channels 1, 2 and 3. It
is not unusual,
especially with television channels, to distort only the channels that are not
allowed to be seen,
while leaving the other channels viewable. Other channels, e.g. data channels
such as Internet
connections, can easily be selected for connection.
In the example given, channels 1, 2 and 3 are a data channel 1 with a computer
5 connected
to it or to be connected to it, a television channel 2 with television
receiver 6 and a separate audio
channel 3 with audio installation 7. Audio installation 7 can be connected to
television set 6 by
connection 0, so that it is also possible to play DVDs.
With interruption and/or distortion unit 4, connections 11 connect a receiving
device 9 to a
signal receiver 10. Receiving device 9 and signal receiver 10 are set to
receive and detect a
previously-determined simultaneously plurality of transmitted infra-red
signals and/or radio signals.
Thcse previously-determined optical (typically infra-red) signals and/or radio
signals are
transmittcd by signal generator 12. The signal gcnerator 12 may therefore be a
set of infrared light
emitting diodes (which may differ in location or orientation, optical
wavelength, polarization, etc.),
and/or radio frequency transmitters (e.g., TTU unregulated frequencies,
including, for example,
6765-6795 kHz, 433.05-434.79 MHz 61-61.5 GHz, 13,553-13,567 kHz, 26,957-27,283
kHz, 40.66-
40.70 MHz 902-928 MHz, 2,400-2,500 MHz, 5,725-5,875 MHz and 24-24.25 GHz).
While
typically, a single modality of communication is used, it is possible to have
both infrared
transmitters and RF transmitters active.
In the example given, signal gcncrator 12 compriscs a housing 13, a plurality
of LEDs 14
that transmit a plurality of optical signals, and a push-button switch that
can be used to transmit the
signal. It is noted that the LEDs 14 may be housed in a single optical
package, similar or identical
to tricolour (R/G)or full color R/G/B LED modules.
Fig. 2 shows signal generator 12 schematically in more detail. In housing 13,
there is a
battery 16 in the form of a button cell, which supplies the whole circuit.
Connections 17 and 18
CA 02689533 2009-12-04
WO 2007/143687 PCT/US2007/070512
Omnizap-201 PCT
-12-
connect battery 16 to a programmable integrated circuit 22. Connection 18
includes a spring-loaded
set of contact points 19, interrupted by a non-conducting strip 20. Strip 20
is provided with a grip
21, to which the strip can be extended between contact points 19. Integrated
circuit 22 is further
connected to LEDs 14 by switch part 23, whereby switch part 23 also has the
components required
to drive LEDs 14. It is, however, also possible to integrate circuit 22 so far
that it can drive the
LEDs directly. Finally, connection 24 with contact points 25 connects push
contact 15 to integrated
circuit 22.
Signal generator 12 can be made extremely small, whereby however a minimum
size will
preferably be adhered to so that signal generator 12 and particularly push
contact 15 can still be
easily operated. One possible size for the top surface of the housing is in
the order of 2 x 3 cm, for
instance. Switching the whole system starts with reversing the interruption in
the power supply to
signal generator 12 by removing the non-conducting strip 20. Next, push
contact 15 is operated, so
that integrated circuit 22 is triggered and LEDs 14 transmit the simultaneous
previously-determined
signals. With infra-red signals, or spatially diverse signals, it is important
that LEDs 14 are properly
aimed in the direction of the signal receiver 10, with sufficient time having
been set, e.g. 30
seconds. After signal recciver 10 detects the simultaneous signals,
interruption and/or distortion
unit 4 is activated to connect and/or pass the incoming c.hannels undistorted.
Here, unit 14 is
programmed for how long the channels are to be made available, e.g. 12 or 24
hours.
The foregoing disclosure of embodiments and exemplary applications of the
present
invention has been presented for purposes of illustration and description. It
is not intended to be
exhaustive or to limit the invention to the precise forms disclosed. Many
variations and
modifications of the embodiments described herein will be obvious to one of
ordinary skill in the
art in light of the above disclosure. The scope of the invention is to be
defined only by the claims
appended hereto, and by their equivalents.
What is claimed is:
